The usual operating temperatures in marine-type engines are on the order of 650.degree. C. Thus, their valves not only have to resist corrosion but also must have sufficient mechanical strength in a heated state to withstand the recurrent impacts to which their heads are subjected when striking the associated valve seats. Stainless and refractory steels do not have the necessary corrosion resistance. Nickel/chromium alloys, especially those with a low carbon content, are more suitable. In the commercially available alloys of this nature, the nickel/chromium ratio generally ranges between about 4:1 and 2:1. Other metallic constituents such as niobium, tungsten and titanium have some anticorrosive effects but do not contribute significantly to the hardness of the alloy at high temperatures.
I have found that a nonferrous alloy containing substantially equal proportions of nickel and chromium, on the order of 30% (by weight) each, are particularly satisfactory from both the mechanical and the chemical viewpoint as discussed above. Such alloys, however, do not readily lend themselves to a forging operation to form a workpiece which can be machined to the requisite shape and dimensions.